The proposed research is a prospective longitudinal study of math skills development in primary school-age children. The broad, long term objectives of this project are to contribute toward understanding early math ability, math disability (MD) and MD subtypes. Toward these objectives, the following specific aims are proposed: (1) To examine early math skills performance in normally-achieving children and in children with a relative weakness in early math skills. Of particular interest is whether distinct profiles corresponding to the Visuospatial, Semantic Memory, and Procedural MD subtypes proposed by Geary (1993) will emerge; (2) to examine cognitive correlates of concurrent ald later math skills performance; (3) to evaluate changes in math performance over time across the different participant groups and as a function of whether a child meets criteria for MD in grade 3; (4) to identify whether girls with fragile X or Turner syndrome manifest a math weakness at ages 5 through 8 years; (5) to identify molecular genetic correlates of early math performance in girls with fragile X; and (6) to examine the association between ADHD and MD. The health-relatedness of the project is its contribution to defining and understanding MD. Models of MD have been proposed, although the core cognitive deficits associated with MD are not fully understood. Enhanced awareness of these deficits and subtypes is important for guiding identification and intervention of MD. The research design includes four groups at risk for MD and a male and female group with normal math achievement. A male and female at-risk group, and normally achieving boys and girls will be drawn from 300 kindergrateners recruited through a local public school district. Two additional at-risk groups will be girls with fragile X or Turner syndrome, disorders for which a math weakness is well substantiated. Cross-sectional data from high functioning males with fragile X, age 5 to 8 years, will be used to further specific math profiles seen in children fragile X. Methods to be used include annual assessments of math reading-related (i.e., semantic memory), and visuospatial skills, administered individually at ages 5 through 8 years. MD criteria will be based on the MD subtypes proposed by Geary (Aim 1). Additional models of MD may be explored, depending on the outcome of the data. Data on anxiety and ADHD behaviors will be examined more fully in year 05, as a function of whether a child meets criteria for MD in grade 3. Growth curve analysis, ANOVA and multiple regression will be employed to address patterns of math and cognitive performance, the relation across math and other cognitive domains, and the change in performance among these domains overtime.